ANSYS Airpak has set the standard in the HVAC industry for simulating room air distribution and thermal comfort since 2000 and delivers technologies that improve the user’s workflow process by letting the user build more computationally efficient and accurate models faster than any other airflow modeling software package. It can greatly enhance computer-aided engineering for ventilation systems.
Intuitive User Environment
ANSYS Airpak has a highly intuitive user environment, which features a model manager, advanced object wizards, alignment tools and four-window simultaneous views. The model manager facilitates the creation, edits, replication and other object functions; assemblies; libraries; and problem/project configurations and settings. Centralized model management allows the user to quickly and easily access different aspects of the model, particularly useful when handling large and complex models. Several advanced object wizards make it easy to build a complex model from scratch in minutes.
 |
ANSYS Airpak model representing the atrium of a small office building |
MCAD import/export
ANSYS Airpak users can import existing CAD geometries in either IGES or DWG/DXF formats. Direct CAD geometry representation is possible. This CAD import feature can be used to directly represent CAD geometries in ANSYS Airpak.
Diffuser Macros
For simulations of room airflow, it is important to accurately model the behavior of air inlet diffusers and thus predict the penetration and spread of the air in the room. This performance aspect of air inlet diffusers is referred to as the throw of the diffuser, which is defined as the distance downstream of the diffuser where the jet centerline velocity equals a specified terminal velocity. Due to the large scale differences between the dimensions of the room and the important small geometrical features of diffusers, it is infeasible computationally to explicitly model the detailed geometry of diffusers. Simply neglecting the geometrical details of the diffuser usually leads to airflow simulations that deliver the correct amount of air into the room, but fail to achieve the proper jet penetration. However, simplified diffuser models that account for diffuser performance or the velocity field in the vicinity of the diffuser exit can be used to predict the penetration and spread of the air jet into the room. ANSYS Airpak includes diffuser macros to help you accurately model several different types of diffusers with simplified boundary conditions.
 |
Round ceiling diffuser airflow path lines colored by air temperature |
Meshing
ANSYS Airpak provides a mixed meshing capability in which the user can utilize mixed tetrahedral and hexahedral meshes. The automatic hex-dominant mesher can be used to mesh geometries quickly and efficiently. It is robust and highly automated, delivering mostly hexahedral elements; it also includes triangular, tetrahedral and pyramidal cells. It uses advanced meshing algorithms to allow the most appropriate cell type to be used to generate body-fitted meshes for the most general geometries.
 |
Non-conformal mesh capability allows the user to vary mesh attributes independent of mesh requirements in adjacent regions |
Turbulence Modeling
ANSYS Airpak provides a mixing-length zero-equation turbulence model, an indoor zero-equation turbulence model, a two-equation turbulence model (the standard k-e model), the RNG k-e turbulence model and the Spalart-Allmaras turbulence model. In most ventilation design cases, the indoor zero-equation model will sufficiently account for the effects of turbulence and addresses the need of users for a simple but reliable turbulence model for room ventilation providing faster computational turnaround due to having less stringent mesh requirements and less mathematical complexity for the model formulation.
Thermal Comfort Related Post-Processing
Several thermal comfort quantities that can be reported include: mean age of air which is the average lifetime of air at a particular location in the room relative to the time when it first entered the room; mean radiant temperature which is defined as the uniform temperature of an imaginary enclosure in which the actual non-uniform enclosure; and relative humidity which is the percentage fraction of water vapor present in the air/water vapor mixture in the room relative to a saturated air/water-vapor mixture at the same temperature.
ANSYS Airpak also uses the ISO 7730 standard concerning the thermal sensation of people to calculate PMV (predicted mean vote) and PPD (predicted percentage dissatisfied) in moderate thermal environments based on air temperature, air velocity, mean radiant temperature, relative humidity or partial water-vapor pressure, activity level, and the amount and type of clothing worn. The user can specify the values used by ANSYS Airpak to compute PMV in the Comfort level calculation panel.
 |
Contours of mean age of air in a hospital patient room |
Visualization and Reporting
Four-window viewing simultaneously displays complex 3-D models from four viewpoints with on-screen iconic view controls to select viewpoints. The user can manipulate the geometry, as well as post-processing views, from different angles since each of the viewpoints are independently controllable. This powerful visualization tool allows the user to efficiently view the results of simulations of complex models to make appropriate design decisions.
 |
Several views of airflow patterns, temperature, and mean age of air for a hybrid office ventilation system employing chilled beams and under floor air distribution (UFAD) |
|
